This invention relates to sensor systems that are cooled during service, and, more particularly, to a structure that reduces "heartbeat" noise reaching the sensor and appearing in the sensor output signal.
A sensor assembly receives radiated energy from a scene, and converts that energy into electrical signals for display and/or analysis. Many infrared and other types of sensor assemblies operate most efficiently and reliably when cooled to a cryogenic temperature, such as about the boiling point of liquid nitrogen, 77K, and are operated in a vacuum to provide thermal insulation for the sensor assembly and to avoid condensation of materials such as water on the sensor assembly. To effect these conditions in service, the sensor assembly is mounted on a platform supported on a hollow tube termed a "cold finger", and within an evacuated dewar/vacuum enclosure. The dewar/vacuum enclosure typically includes an insulated vacuum housing having a window through which the sensor views an external scene.
When the sensor is to be used in service, the opposite end of the cold finger is cooled by a cooling device, causing heat to flow out of the cold finger, the platform, and the sensor assembly. After the sensor assembly reaches the required reduced operating temperature, it becomes operational.
When the sensor is operated, the image produced by the sensor output signal is typically degraded by a periodic type of noise termed "heartbeat". The sensor is operable even in the presence of the heartbeat noise, but the resulting image is either used in a degraded form or must be digitally processed to reduce the heartbeat noise. Digital processing utilizes computer resources that are otherwise better used elsewhere, and slows the processing of the image.
There is a need for identifying the source of the heartbeat noise, and reducing or eliminating the heartbeat noise from the sensor output signal. The present invention fulfills this need, and further provides related advantages.